Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $50.45   9.528%   $55.2569   $55.26   $55.25   $55.30  
  Purchase #2 $15.87   3.487%   $16.4234   $16.42   $16.40   $16.40  
  Purchase #3 $19.74   12.257%   $22.1595   $22.16   $22.15   $22.20  
  Purchase #4 $141.34   4.426%   $147.5957   $147.60   $147.60   $147.60  
  Purchase #5 $79.31   13.711%   $90.1842   $90.18   $90.20   $90.20  
  Purchase #6 $119.90   7.260%   $128.6047   $128.60   $128.60   $128.60  
  Purchase #7 $222.40   3.206%   $229.5301   $229.53   $229.55   $229.50  
  7 purchase totals = $649.01       $689.7545   $689.75   $689.75   $689.80